Which of the following complexes is not a chelate?

Options

A. bis(dimethylglyoximato)nickle(II)
B. potassium ethylenediaminetetrathiocyanatochromate(III)
C. tetraamminediazidocobalt(III)nitrate
D. trans-diglycinatoplatinum(II)

Answer

To determine which of the given complexes is not a chelate, we need to understand the concept of chelation and the types of ligands involved in each complex. A chelate is formed when a ligand binds to a central metal atom at multiple points, creating a ring-like structure. Ligands that can bind at two or more sites are known as bidentate or polydentate ligands, while those that bind at only one site are called monodentate ligands.

Let's analyze each option provided in the question:

1. **20 Dimethyl Glyoxamato (DMG)**: This ligand is a bidentate ligand because it can bind to a metal at two different sites (the two oxygen atoms). Therefore, complexes formed with DMG are chelates.

2. **Potassium Ethylene Diamine Tetra Thio Cyanatochromate**: Ethylene diamine is also a bidentate ligand, as it has two nitrogen atoms that can coordinate to a metal center. Thus, this complex can form a chelate.

3. **Tetra Amine Dioxodicobalt(II) Nitrate**: The amine ligands (NH3) are monodentate ligands. Since all ligands in this complex are monodentate, they cannot form a chelate structure. Therefore, this complex is not a chelate.

4. **Trans Di Glycinato Platinum(II)**: Glycine is a bidentate ligand because it can bind through both the amino group and the carboxylate group. Hence, this complex can also form a chelate.

Based on the analysis above, the complex that is not a chelate is:

**Answer: Tetra Amine Dioxodicobalt(II) Nitrate (Option C)**

### Step-by-Step Solution:
1. **Understand the concept of chelation**: A chelate is formed when a ligand binds to a metal at multiple points, creating a ring structure.
- **Hint**: Remember that chelation involves multi-point attachment of ligands to a metal.

2. **Identify the ligands in each complex**: Analyze each option to determine whether the ligands are monodentate or bidentate.
- **Hint**: Look for the number of binding sites each ligand has.

3. **Evaluate each complex**:
- **Option 1**: DMG - Bidentate (chelate).
- **Option 2**: Ethylene diamine - Bidentate (chelate).
- **Option 3**: Tetra Amine Dioxodicobalt(II) Nitrate - Monodentate (not a chelate).
- **Option 4**: Glycinato Platinum(II) - Bidentate (chelate).

4. **Conclude which complex is not a chelate**: The complex with only monodentate ligands cannot form a chelate.
- **Hint**: Identify the option with only monodentate ligands.

5. **Final Answer**: Tetra Amine Dioxodicobalt(II) Nitrate (Option C) is not a chelate.